Some of this can be attributed to socialization or the lack thereof. But a lot of it is also just poor breeding practice.
My best dog ever was a yellow lab. And he did well around other dogs in the field, but could, in the right circumstance be aggressive towards people. He was this way despite extensive socialization. No one was surprised as the bitch that he was bred from was the same way.
OTOH, I never worried about anyone breaking into my home. Actually had a mentally ill guy walk in one day. Seems he had a rep for doing just that around town. The cops joked that my dog might have cured him of it.
